A new calibration of Galactic Cepheid period-luminosity relations from B to K bands, and a comparison to LMC relations^*

¹ Observatoire Midi-Pyrénées, Laboratoire d'Astrophysique, UMR 5572, Université Paul Sabatier - Toulouse 3, 14 avenue Edouard Belin, 31400 Toulouse, France e-mail: pfouque@ast.obs-mip.fr
² Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Campus San Joaquín, Vicuña Mackenna 4860, Casilla 306, Santiago 22, Chile
³ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁴ University of Texas at Austin, McDonald Observatory, 1 University Station, C1402, Austin, TX 78712-0259, USA
⁵ currently on assignment to the National Science Foundation, 4201 Wilson Boulevard, Arlington, VA 22230, USA
⁶ Max-Planck-Institut für Radioastronomie, Infrared Interferometry Group, Auf dem Hügel 69, 53121 Bonn, Germany
⁷ Center for High Angular Resolution Astronomy, Georgia State University, PO Box 3965, Atlanta, Georgia 30302-3965, USA
⁸ Observatoire de Paris-Meudon, LESIA, UMR 8109, 5 place Jules Janssen, 92195 Meudon Cedex, France
⁹ Universidad de Concepción, Departamento de Física, Grupo de Astronomía, Casilla 160-C, Concepción, Chile
¹⁰ Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD, UK

Received: 29 June 2007
Accepted: 15 September 2007

Abstract

Context.The universality of the Cepheid period-luminosity (PL) relations has been under discussion since metallicity effects were assumed to play a role in the value of the intercept and, more recently, of the slope of these relations.

Aims.The goal of the present study is to calibrate the Galactic PL relations in various photometric bands (from B to K) and to compare the results to the well-established PL relations in the LMC.

Methods.We use a set of 59 calibrating stars, the distances of which are measured using five different distance indicators: Hubble Space Telescope and revised Hipparcos parallaxes, infrared surface brightness and interferometric Baade-Wesselink parallaxes, and classical Zero-Age-Main-Sequence-fitting parallaxes for Cepheids belonging to open clusters or OB stars associations. A detailed discussion of absorption corrections and projection factor to be used is given.

Results.We find no significant difference in the slopes of the PL relations between LMC and our Galaxy.

Conclusions.We conclude that the Cepheid PL relations have universal slopes in all photometric bands, not depending on the galaxy under study (at least for LMC and Milky Way). The possible zero-point variation with metal content is not discussed in the present work, but an upper limit of 18.50 for the LMC distance modulus can be deduced from our data.